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FreeBSD-SA-19:06.pf                                         Security Advisory
                                                          The FreeBSD Project

Topic:          ICMP/ICMP6 packet filter bypass in pf

Category:       contrib
Module:         pf
Announced:      2019-05-14
Credits:        Synacktiv
Affects:        All supported versions of FreeBSD
Corrected:      2019-03-21 14:17:10 UTC (stable/12, 12.0-STABLE)
                2019-05-14 23:12:22 UTC (releng/12.0, 12.0-RELEASE-p4)
                2019-03-21 14:17:12 UTC (stable/11, 11.3-PRERELEASE)
                2019-05-14 23:12:22 UTC (releng/11.2, 11.2-RELEASE-p10)
CVE Name:       CVE-2019-5598

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

pf(4) is an Internet Protocol packet filter originally written for OpenBSD.
In addition to filtering packets, it also has packet normalization
capabilities.

II.  Problem Description

States in pf(4) let ICMP and ICMP6 packets pass if they have a packet in
their payload matching an existing condition.  pf(4) does not check if the
outer ICMP or ICMP6 packet has the same destination IP as the source IP of
the inner protocol packet.

III. Impact

A maliciously crafted ICMP/ICMP6 packet could bypass the packet filter rules
and be passed to a host that would otherwise be unavailable.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.
Afterwards, reboot the system.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Afterwards, reboot the system.

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-19:06/pf.patch
# fetch https://security.FreeBSD.org/patches/SA-19:06/pf.patch.asc
# gpg --verify pf.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r345377
releng/12.0/                                                      r347593
stable/11/                                                        r345378
releng/11.2/                                                      r347593
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://www.synacktiv.com/posts/systems/icmp-reachable.html>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5598>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:06.pf.asc>
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